The invention relates to a protective switching device, and in particular to a differential-current circuit breaker, having a core-balance transformer which monitors a line network and which, via a tripping circuit and an actuation circuit, actuates a release which is coupled to a switching mechanism in order to operate a power breaker.
Such a protective switching device is described in (U.S. Pat. No. 4,001,646). The protective switching device is used to ensure protection against a dangerous body current in an electrical system. For example, when someone touches a live part of an electrical system, the fault current then flows via the person as a body current to ground. The circuit breaker which is used for protection against dangerous body currents safely and rapidly isolates the relevant circuits from the mains power supply when the so-called rated fault current is exceeded.
The construction of a circuit breaker is described, for example, from xe2x80x9cetzxe2x80x9d, Volume 107 (1986), issue 20, pages 938 to 945. There, FIGS. 1 to 3 in particular show basic circuit diagrams and functional principles of a fault-current circuit breaker (FI circuit breaker) and a differential-current circuit breaker (DI circuit breaker).
FI and DI circuit breakers are constructed in a similar way from three assemblies. A core-balance transformer, through whose transformer core all the current-carrying conductors of a line network are passed induces a voltage signal in its secondary winding in the event of a fault current, and this voltage signal actuates a release which is connected to the secondary winding. For its part, the release is coupled to a switching mechanism via which, when the release is operated, the contacts of a power breaker connected in that line or in each line are opened. In the process, the FI circuit breaker draws the energy required for tripping from the fault current itself, irrespective of the mains power supply voltage, while tripping in the case of a DI circuit breaker takes place as a function of the mains power supply voltage. To this end, when a fault current occurs in the electrical circuit supplied from the line network, the signal emitted from the core-balance transformer is supplied, after amplification by means of an electronics unit that is dependent on auxiliary energy, to the DI tripping circuit of the DI circuit breaker or DI accessory.
A test device having a test button is provided for checking the serviceability of such a protective switching device for circuit breaker, which test button is normally connected between the neutral conductor (N) and a phase conductor (L1, L2, L3) of the line network. When the test button is pressed, a fault current is simulated, and the reaction of the circuit breaker is tested. In this case, the circuit breaker must trip with virtually no delay when in the serviceable state.
Furthermore, a remote release is frequently provided in such circuit breakers, via whichxe2x80x94for example for disconnectionxe2x80x94the circuit breaker and thus the power breaker coupled to it can be operated externally. In order to provide a remote release for a DI circuit breaker, one option is for a mate contact to be connected in parallel with the test contact via a remote tripping line connected to said DI circuit breaker. Another option is for a separate winding to be provided in addition to the test winding on the core-balance transformer. The separate winding is connected between two external conductors or between one phase conductor and the neutral conductor via a current limiting resistor, for operation of a remote tripping switch. These two versions for remote tripping on the one hand also require at least one auxiliary contact, however, in a disadvantageous manner. On the other hand, the feeders to the remote tripping switch and the switch contact for the remote release must be designed for a particularly high withstand voltage.
In the case of a DI accessory for power breakers, an additional exacerbating factor is that no auxiliary contacts can be provided owing to the switching paths accommodated in the power breaker. Since such circuit breakers are also designed with three poles, a connection between two outer conductors would also be required. Furthermore, a particular feature of DI circuit breakers or accessories is that tripping time delays of up to one second can frequently be set. Thus, if the remote release were operated according to the said variance, a relatively long tripping time would have to be taken into accountxe2x80x94depending on the time delay setting. However, this is unacceptable with regard to emergency disconnection.
In one embodiment of the invention, there is a protective switching device including a corebalance transformer which monitors a line network and actuates a release which, via a tripping circuit and an actuation circuit, is coupled to a switch mechanism in order to operate a power breaker, wherein a tripping circuit, which can be tripped by a remote tripping signal, is connected to a transformer which can be actuated on the secondary side and whose primary side is connected to an actuation circuit of the release.
In one aspect of the invention, if the secondary of the transformer is short-circuited, the tripping circuit produces a control signal for the actuation circuit of the release.
In another aspect of the invention, the tripping circuit comprises an oscillator which is connected to the primary side of the transformer.
In yet another aspect of the invention, the oscillator is a square-wave generator whose frequency is set to between 500 Hz and 5 Hz.
In still another aspect of the invention, the protective switching device wherein the tripping circuit has a comparator which is connected on the primary side to the transformer and is connected on the output side to the actuation circuit for the release.
In another aspect of the invention, the protective switching device wherein the tripping circuit has a non-reactive resistor
RS greater than 10 kxcexa9 which is connected to the primary winding of the transformer.
In another aspect of the invention, the tripping circuit has a reference signal source having a voltage divider which is fed from a supply voltage, via a zener diode.
In yet another aspect of the invention, a secondary of the transformer is connected to ground potential via a resistor series circuit.
In still another aspect of the invention, the actuation circuit comprises a comparator with a downstream controllable electronic switch, which is connected to the release.
In yet another aspect of the invention, the controllable switch is a transistor whose base control input is connected to the comparator and in whose collector-emitter circuit a tripping relay coil of the release is connected.